Automatic flight control system



0t l 1953 s. LENEFsKY E'rAL 3,105,660

AUTOMATIC FLIGHT CONTROL SYSTEM 3 Sheets-Sheet 1 Filed 0G19. 4, 1960 .65200 momdwn M255 Illlllllll E/SEN mmOlxO-a KY MORRONE INVENToRs E/VEFS SOS@ MEE Iota n Nm. rlllll ATTO NEY Oct. l, 1963 s. LENEFsKY ETAL AUTOMATIC FLIGHT coNTRoL SYSTEM 3 Sheets-Sheet 2.

Filed Oct. 4, 1960 .NGE

lllll| DON/4L REFFE/SE/V ATTO NEY Z Oct. l, 1963 s. LENEFsKY ETAL 3,105,660

AUTOMATIC FLIGHT CONTROL SYSTEM 3 Sheets-Shea@ 3 Filed Oct. 4, 1960 QWNN i NN

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United States Patent O 3,105,660 AUTOMATIC FH'GHT CGNTROL SYSTEM Selig Lenefsky, New Hyde Park, John Morrone, Eimhurst, and Donal R. Trefeisen, Huntington Station, N Y., assignors te Sperry Rand Corporatien, a corpo= ratien of Delaware Filed Oct. 4, 1960, Ser. No. 60,412

13 Claims. A(Ci. 24e- 77) This invention relates generally to flight control systems and more particularly to apparatus for controlling the iiight of a vertical take-off and landing, i.e. VTOL, aircraft during a landing maneuver. Y

The landingof a VTOL aircraft is a unique operation because aerodynamic forces which support the craft above the earth during normal flight must be gradually replaced by the thrust of the craft engine as Vthe landing area is approached.- Generally, this exchange of support forces is achieved by decreasing the ground speed of the VTOL craft to zero and, at the same time, precessing the resultant thrust of the craft so that it has a perpendicular relationship with the earth. When the VTOL craft being landed is a tailsitter, i.e. the type that takes off and lands with its longitudinal axis perpendicular to the earth, the ground speed reduction and thrust precession may be attained by gradually increasing the craft flight path angle to ninety degrees while, at the same time, increasing the thrust until a thrust-to-weight ratio of one is attained. This causes the craft to zoom to a considerable height above the earth. The craft is then backed down to the earth by carefully manipulating the craft throttle. The backing-down operation is an extremely fatiguing one for the pilot because of the care with which he must control the throttle. In addition, the backing-down operation is extremely ineicient because the craft thrust must be held approximately equal to the craft weight to effect a safe descent rate. This results in high fuel consumption.

Apparatus embodying the present invention minimizes pilot fatigue and improves the eiciency of landing a tailsitter VTOL craft by eliminating the need for` a zooming maneuver, thereby lowering the altitude at which the backing-down maneuver must be started. Generally, the zooming maneuver is eliminated as follows: with the craft in normal level flight, i.e. flying as a conventional airplane, and approaching a landing area, the craft thrust is reduced to a predetermined low level. At the same time, the craft pitch is gradually increased to maintain the L PatentediOct. Vl, 1963 consumption by shortening the backing-down maneuver required, as earlier discussed, and by causing the craft to iiy'through a considerable portion (the initial phase) of the landing maneuver at a low thrust level.

' Throughout the'abvefdescribedphase of the landing maneuver the craft attitude 'relative to the earth must be changed constantly; therefore, each of the craft control surfaces must-be constantly varied relative to some neutral position (as defined by a reference device) to eiectthese attitude changes. Most prior art referenceV devicesare slaved to the earth andas such establish references which have fixed orieutationsrelative tothe earth. When an aircraft employs one of rthese reference devices, e.g. a gyro horizon, and acquires a pitch attitude of 90 degrees, the roll axis pick-off and yawfaxis pick-olf of the deviceV both producey meaningless output signals. This is because the gyro is in gimbal lock. Evenwith single degree of freedom gyros, theV coordinate transformation that takes place at a pitch angle of 90 .causes a change of control sensing. A roll axis pick-offl produces a signal representing the yawof the craft and a yaw axis pick-off produces a signal representing the roll of the craft. Since the tailsitter VTOL aircraft often has a pitch attitude of 90 degrees, apparatus embodying the invention does not employ a fixed reference, but, instead, varies the attitude of the reference relative to the earth. The craft control surfaces are then varied'relative to varying neutral positions as defined by the varying reference. In this way, the craft pitch angle relative to the reference isfm'aintained considerably below 90 degrees, thereby avoiding the problem encountered with fixed reference systems. To provide a reference having a variablev attitude, the -presentinvention employs a two-degree of freedom gyro whoseprecessable spin axis defines thereference and the instantaneous commanded attitude of the craft longitudinal axis. That is, the gyro spin axis is first directed. asdesired and the craft is made to follow-up on this moving referf ence, thereby keeping the pitch command signals (and the angles that they represent) small. Since .yaw and roll control of the craft constitute no part of the invention,

they are not discussed in this specification.

With the craft hovering Aand ready to descend to the earth, changes in thecraft lateral position over the earth rare made generally as followsrthe craft resultant thrust vector is simultaneously tipped and increased to produce two components of thrust, one component being 'in the direction that the pilot desires to move the craft and the craftaltitude constant; this causes the craft angle of attack Y thrust-to-weight ratio of approximately one is reached.

The throttle is advanced before reaching the stall angle of attack so that the thrust increase (which lags the advance of the throttle) produced thereby will exactly coincide in time with the loss of aerodynamic lift experienced at the stall angle of attack. At the same time the throttle is being advanced, the craft thrust is deflected from a substantially parallel relationship with the craft longitudinal axis to keep the craft pitching up until a pitch attitude of approximately ninety degrees is reached. Thrust deflecting techniques presently employed by VTOL aircraft utilize: pivotably mounted engines; vanes which are insertable into the exhaust stream from the craft engine; and auxiliary engines, different combinations of which effect different directions of resultant thrust. Whereas the prior art technique for landing a tailsitter VTOL craft requires the craft throttle to becontinually advanced to zoom the craft to a considerable distance over the earth, apparatus embodying the, invention enables thel craft to be positioned a short distance over 'the earth through a retard-then advance manipulation of the craft throttle. Such throttle control provides economical fuel Just prior to reaching the stallv othercomponent being equal to the craft weight `.and

' directed perpendicular to therearth. The resultant thrust vector of the craft is tippedthrough the operation-of the craft thrust deector which,/as presently .practiced in the art, is varied by an amount proportional to the force applied to the craft control stick. By varying the craft` thrust deflector, forces are produced which tend to tip and angularly accelerate the craft about'its pitch axis. In order for the pilot to control the laterall positioning of his craft over the earth, it is necessary for him first to perform mentally a double integration'of this angular acceleration to determine thelproper angular orientation of the craftabout its pitch axis. Then, with'this angular orientation determined and producing a thrust component position.. As a resultY of these mental integrations, the pilot derives a signal representing the time integral ofthe craft lateral velocity, i.e. thelateral distance that the craft has moved, and' adjusts the'force'applied 'to his control stick in proportion to this signal. For example, withthe craft moving at a given velocity toward a desired position, the pilot must derive mentally the distance covered relaf thrust componentfto bring thecraft to tive to that position and move his control stick to slowl amasar f once again doublyv the craft down as the position is approached. This is so that the completed integration of the craft velocity with respect to time will leave the craft in the exact position desired. Mentally performing simultaneously two double integrations is an extremely difficult job for the pilot and, therefore, it is very difficult for him to derive a signal (representing lateral distance covered) which can be used to cancel the signal representing the force applied to the control stick.l Therefore, in practice, the pilot in order to change his lateral position momentarily moves his control stick and immediately retracts itv to its neutral position. This causes the craft to inch towardV the desired lateral position, This is repeated time reaches the desired position. This ,control problem is made more difficult because of the excessive lag between control action and desired response. In generahsuch a control system would be unstable when in the hands of the pilot.

Apparatus embodying the invention simplifies the job of the pilot by eliminating some of the integrations which the pilot heretofore had to perform mentally. In one specie of the invention, a signal representing the result of integrating the craft angular velocity in pitch, i.e. angular position or lateral acceleration, is automatically provided and compared with asignal representing the force applied to the control stick to produce an error signal. The error signal is then used to vary the craft thrust'deflector until aftertime until the craft y Y i I stituted for a circuit in-FIG. 1 to provide a dlferent'ema signal representing an angular orientation of the craft about its pitch axis and exactly cancelling the control stick force signal has been produced, Therefore, the pilot commands an angular orientation of the craft about its pitch axis when'he moves his'control stick and has only to perform mentally a double integration of a signal representing the craft lateral acceleration to derive a signal representing the distance that the craft has moved. This derivedv signal, in the form of a force, is then subtracted from the force applied to the control stick. This `entire operation can be done with comparative ease since the pilot is required to perform only one double integration, thereby obviating the need to inch the craft over to a new position as earlier mentioned.

Another specie of the invention automatically provides and compares a signal representing the craft lateral velocity with a signal representing the force applied to the craft control stick to produce an error signal.V The error signal is then used to varyfthe craft thrust deflector until a signal representing the craft velocity is produced which cancels the control stick force signal. Thus, with this specie, when the pilot moves his stick he commands a lateral velocity. Thepilot, therefore is requiredto integratel (mentally) only the craft lateral velocity to derive a signal representing the lateral distance that the craft has moved. This signal, as before, in the form of aforce is then subtracted from the force applied to the control stick.

While a system which automatically provides-and compares a signalrepresenting the time'integral of lateral velocity, i.e. lateral distance covered, with a signal representing the force applied to the craft control stick has not been discussed, it is Well within the purview of the invention. In such a system, the pilot would command a lateral position when he moves his control stick. This type system, however, has the limitation that some means for bringing the craft Within a close range of the landing area would be required. Thisis because situations could `arise wherein the stick, even though it had been moved the .full extent of its travel, could only direct the craft to a position short of the position desired. a

- A principal object of the invention is to provide landing control apparatus for VTOL tailsitter aircraft;

Another object of the invention is to provide apparatus for controlling the night of a tailsitter VTOL craft through its stall angle of attack;

Another object of the invention is to provide apparatus for controlling the lateral position over the earth of a VTOLcraft while the craft is in hovering night.

p The invention will be described with reference to the drawings of which: Y FIG. 1 is a block diagram of one form of the invention; f

control useable with the invention;

FIGS.V 3a, 3b and 3c, are diagrams showing 'typical landing maneuvers made possible by 'the present invention; V PIG. 4 is a blockdiagram of a circuit which,` when substituted for a circuit. in FIG. l, provides another embodiment of the invention; and v FIG. 5 is another block diagramwhich maybe subbodiment of the invention. Y

Referring to FIG. 1,5*a radio altimeter 10, produces Aa signal representing the instantaneous altitude of the craftl This signal is applied to a diferentiating circuit' 12 which produces a signal representing the craft rate of descent,

the descent rate'signal then being applied to a summing` circuit' 14. A signal representing a vreference rate of descent is also applied to tbe'sumrning circuit 14 and is provided by an altitude'rate reference 16 whchmay be a simple potentiometer. The signal provided by-the refer- Y ence 16 is suchthat Vit has a sense opposite to that of the Y differentiating circuit 12 output signal when the craft' descends at the reference rate." Therefore, whenthe actual and reference descent rates are equal, the summing circuit 14 does not produce an altitude rate error signal. Any

signal which is produced by the summing circuit 14, how` ever, n is applied through switching (the description -of which will follow) to an amplifier 18. I

The amplifier 18 output signal is then used to precess the spin axis of a two'degree of freedom gyro 20 which provides the craft with a variable Vattitude reference asi f earlier described. A torquer 22, mounted 'on-the, gyrok 2i), precesses the gyr'o spin axis about an-axis parallel to the craft pitch axis in proportion Vto signals applied` to it by the amplifier 18 by applying, in accordance Vwithrwellknown gyroscope principles, a torque which tries torotate'` the gyro spinaxis about an axis parallell tov the craft yaw axis. For clarity, only one torquer is shown in FIG'. `l., 1

since the present invention is concerned primarily with the pitchV attitude of the craft.

which are simultaneously closed by vthe pilot when 4he Wants to land his craft,'op erate toenergize a relay 26,

When the relay 26 is energized, the switches 26m-2612, l26a" Qy and v25d all move to their lower positions. "With the switch 26a in its lower position, a` signal representing a predetermined low thrust level is applied from aV thrust reference 28, which maybe a simple potentiometer, to'.V an amplifier 30.K4 The amplifier 30V then applies its output y signal to a servo 32 which drives, through aslipclutch",

34 and differential gearing 36, the thrust varying means of the craft. The craft throttle`control37 isalso ,con-` nected to the craft thrust varying means throughthe gearing 36.

A `stall detector 38, preferably similar to one ofthe;

stall detectors disclosed in U.S. Patent 2,891 ,1742, issued in the name of D. R. Treleisen et al., and assigned tothe` assignee' of the presentinvention (see elements 69 and With the switch 2Gb in ,its upper positiomanyjaltitude rate yerror signal appearing at the output of the summing y circuit 14 is applied, to the -ampler -30 so tliat'altitudel rate cangbe commanded through the craft'thrust control-f system aftery the craft stal-l angle of --attack is Vreached. When the switch 4Gb closes, a pitch ratetreferencei2Y` FIG. 2 is a block diagram of an elevator and thrust A pair of manually'operated` switches 24a andv24b,y

. craft. Hence,

(which also may be a simple potentiometer4 thatY can be preset by the pilot or in accordance with the design of the craft) applies a signal representing a commanded pitch-up' craft has a pitch rate to the `amplifier 18. When the yattitude slightly greater than ninety degrees, a pitch rate cutout device 44 produces a signal which is applied to a self-holding relay 46 which removes the pitch rate reference 42 signal from the amplifier 1S by opening the switch 46a. The pitch rate cutout 44, whichvmay be a simple pendulum or a pick-off on a gyro horizon, energizes the relay 46 at pitch attitudes greater than ninety degrees to provide braking for the craft, i.e. reducing the craft ground speed to zero, by means of the craft thrust. Thiswill-be described morerfully later.

'As the craft goes through. the landing maneuver, its ground speed isV decreased -by decreasing the craft thrust, by changing the direction of the craft thrust from a parallel `relationship with the earth, and by lbraking the craft with the craft thrust. A ground speed computer 48 providing a signal representing the craft ground speed applies thisk signal to a comparison circuit 50 together with a signal representing some low ground speed reference (usually zero feet per second), the latter signal being derived from `-a ground speed reference device 452. `In

practice, the signals provided by the ground speed computer 48 and radio altimeter 16 both maybe provided by a single device such as pulsed doppler radar. The comparison circuit 50 produces an output signal whenever the CII lactual ground speed of the craft equals the reference Y ground speed. A typical comparison circuit useable in thismannerris shown and describedkin the Massachusetts Institute -of Technology Radiation Laboratory Series, vol.

1.9, page 343, FIGS. 9-20, McGraw Hill Publishing Company, Inc., 1949. When the comparison circuit 50 pr oduces an output signal, it applies that signal to a self-holding relay 54 which remains energized after the comparison circuit output signal is removed, thereby holding switches 54a and 54h in their lower positions. When the switch 54a moves to its lower p-osition, signals, if any, representing long term departures of the craftlongitudinal axis from a vertical relationship with the earth are `applied from avertical reference 56, e.'g. a damped pendulum, to the amplifier 18. Since there is a three degree departure of the craft longitudinal axisfrom the earth vertical at this time, the gyro 20 spin axis (and therefore the craft longitudinal axis) is precessed to a vertical relationship with the earth t-o cancel the reference S6 output signal.

Prior to initiating the :landing maneuver, signals derived 4from the craft control lstick are applied to the torquer 22 and the pilot, in effect, flies the reference when he moves his stick. The craft then follows up on the reference as was mentioned earlier. In conventional pitch control systems, i.e. systems in which the control stick directly controls the deflection of the craft elevators, the amount that the control stick mustbe deflected to effect a given craft pitch rate varies inversely with the speed of the for naturalness of feel, it is important to have the reference fly in response to control stick comrnands exactly the w y an airplane would y. A control stick pick-off 58, responsive to the application of force to the control stick 60, produces a signal proportional to that force. This signal and a signal derived from the craft air speed computer 62 are applied toa divider circuit 64 which produces a signal proportional to the ratio of the control stick force to the craft air speed.`` Usually, the air speed signal is limited to some value greater than zero to prevent division -by zero during hover. The divider 64 output lsignal is then applied through the switch Sli-b tofthe amplifierlS when the switch 54]: is in its upper position, i.e. prior to slowing down to the reference ground speed. Once the switch 54h moves to its lower position, i.e. when the craft slows down to the reference ground speed, the control stick pick-off 58 signals are applied directly to the amplifier 18. Also, whenever a force is applied to thecraft control stick, a normally closed `spring loaded switch-57 is opened to remove theV vertical referencesignal from the amplifier 18. yTherefore, in the final phase of the landing maneuver, the control stick alone controls the attitude of the reference 20.

When there isk anrangular displacement between the gyro spin axis and the craft longitudinal axis, 4e.g. when the spin axis is being precessed away from thecraft longitudinal axis, a pick-olf 66 responds to produce a signal proportional to such displacement. Thepick-otf 66 output signal isalgebraically summed in a Isumming device 68 with a signal which is proportional to the angular acceleration of the craft about the craft pitch axis. This last-mentioned signal is produced by an accelerometer and lag network 70 and serves not only Vto damp the response of the craft to the displacement `signal but to anticipate short term departures of the craft from the attitude defined 'by the spin axis. The output signal from the summing device 68 is applied to a thrust deflector and elevator control 72 which is shown in detail in FIG. 2. The thrust -deflector and elevator control 72 has two channels, one for the control of the craft elevators and .one for the control of the craft thrust deflector. The elevator control channel comprisesan amplifier 74 and a servo '76 which responds to the output signals from the amplifier "74 to operate the elevators.' The lthrust-.deflector channel compri-ses a variable gain `amplifier 78 'and a servo 30 which operates to vary the direction `of the craft thrust in accordance with the amplifier 78 output signals. The

air speed computer 62 connects to and drives rthe wiper :of a potentiometer 82in proportion to the air speed of the craft. The potentiometer 82 output signal is applied to the variable gain amplifier 78 and operates to bias the amplifier 82 so that, yas the craft speed decreases, the out put of the amplifier 78, and therefore theV4 effect of the thrust deflector channel, is gradually increased fromy zero.

vIn. operation, the pilot moves Vthe switches 24a and 24h to their lower positions when he wants to land his circuit 14 which passes through the switches 24th yand 26e to `the amplifier- 18 to precess fthe gyro l20' and thereby cause the craft 'to increase its angle ofv attack, i.e. rate of descent control is maintained through pitch angle. As

fthe craft angle of attack increases,so does the craft lift;

therefore, the craft is able to hold the` reference descent rate even though the craft thrust had been decreased. With the craft reference descent rate equal to zero feet per seco-nd the craft will hold substantially the altitude at which the landing maneuver was started and will therefore have a `landing maneuver profile similar to that shown in FIG.' 3a. If, however, the craft reference descentrateis greater or less than zero 'feet per second, the craft will have landing maneuver profiles similar to those respectively shown in FIGS. 3b and 3c. In either of these latter cases, means v(not shownymust` be provided t-o command a kzero descent rate. when lthe craft goes be-` low, or climbs above, a predetermined altitude, or when .the ground speed vdecreases to zero. This is so -that the craft will neither Vcrash into the ground at the greaterthan-zero reference descent 'rate or ftude at the less-than-zero reference descent rate.

When Ythe actual angle of attack of the craft equals and exceeds the craft stall angle of attack, the gyro 2liI is no zoom to a' high alti-` f plying the altitude rate error signalV from the` summing circuit 14 -to the amplifier 30 in the engine thrust control loop.- Since the craft engine (thrust cannot be varied` instantly in response to' signals applied to the amplier 30, there is a momentary increase in the actual descent rate over the reference descent rate, thereby causing slight lloss in altitude as the craft is precessed through its stall angle of attack. However, this is not a problem if theV tothe output signal from the thrust reference 141, will exactly equal the thrust vlevel commanded by the summing p lcircuit -114 when the switch 150e moves to its lowerpo'si-g y tion. In this way altitude will be neither gained n'oi lost 1- k while prece'ssing through the stall angle Yof attack. f

With the circuit of'FlG. 5 subs ituted for the circuit '200 of FIG. l, three different lateral positioning control Y Y techniques forV the .hovering craft 'are possible.` V.A sumand, when the craft ground speed reaches zero, the gyro 2 0 spin axis is processed back up to a true'vertical relationship with the earth by slaying it to the long term vertical reference 56.

Wit-h'the craft longitudinal axis perpendicular to the earth and the craft ground speed zeno, the craft may have its lateral position relative to the earth varied'by tipping the craft resultant thrust vector (as earlier described) by applying signals from the pick-off 5S to the amplifier d8. Then with the craft hovering over the landing area, thegcraft is lowered to the earth by retarding carefully the throttle control 37 to reduce the craft thrust-to-weight ratio to some value below one. When,

however, the throttle control 37 is released, it immediately advances to the position it` had before it was retarded and the craft holds velocity.

By substituting the circuit shown in FIG. 4 for the circuit 100 of FIG.' l, 4au embodiment #of the invention may be obtained which prevents the craft Ifnom losing altitude while precessing through the craft stall angle ofattack. In FIG. 4, circuit elements 10, 12, 14 `and `16 openate exactly as they did in FIG. 1 and are shown onlyzfor clearness of description. A manually operated switch 24, which is closed by the pilot when he wants lto land his craft, operates Ito energize a relay 126. When the relay 126 is energized, the switches 126e and 126b both move to their upper positions. As a result, a signal produced by the thrust reference 2S', which represents a low thrust level, appears at terminal D 1and an altitude rate error Y signal (if any) .appears at terminal C. The thrust reference' .28' may be a simple potentiometer. When error signals appear on terminal C, the craft pitches up (las described earlier), thereby causing the craft to approach its stall angle of attack. lust prior to reaching the craftV stall angle of attack, a stall detector 3S', which may be similar to the stall detector 3S, but which must be set to respond at an angle of attack slightly less than lthe stall angle of attack, produces an output signal which energizes a relay 140. When the relay 14u is energized, it closes a switch 14th:. This applies a signal produced by a thrust reference 141 and representing a high thrust level (usually about S0 percent o f the craft weight) to the terminal D. At the same time that lthe high thrust level signal is applied to the terminal D, it is also applied to relays 142, 144 and 15th-through a delay device 146. When the relays 142, -144 and 150 become enengized, they respectively -open switches 142a and 144a, yand move a switch 150e to itslower position. Therefore, when the craft throttle control 37 Vis advanced by the application of la level signal to terminal D, the craft mate of descent is still controlled by the signal appearing on terminal C, i.e. by processing the gylro spin axis. However,

trol signals yare removed from theter-minal C and applied to the terminal D `thtuough the'operati-on of the relay `142 (which deenengizes the relay `126 by opening the switch 142a) and through the operation of the relay 150 (which moves the switch 150a to its lower position). 'Ilhe time delay provided by the delay device 146-is set so that theY level of the engine thrust, which is increasing in response r after the lagging thrust builds up, the rate of descent conv integrate mentally the ming circuit 202 which produces a signal representing the difference between Iits linput signals has thepic'kplf V53V output signal .applied to it. A three positionswitchZM- also applies to the summing circuit 202 a signal'representing the angulardepalrture or 3). vThe signal representing the angular departure Yof the craft longitudinal axis from van earth verticalrnay bef provided by a igyro horizon; be provided by the ground the switch is in position 2,

the ground speed signal may:V

position 2, the circuitof the circuit 200 of FIG. lateral position must perform two double vi'nteg'rations a desired position. pilot commandsV a latenal velocity for moves his craft when he this form of lateral positioning control, the pilot must only to a desired position. It is `to be noted that the above described lateral positioning control techniques are not Y. only applicable with tailsitter VTOL cna-ft, but are equally, l applicable to VTOL craftthat lland with their longitudinal to the earth. However, with axes substantially horizontal such craft, the gyrc horizon must provide a signal repre'- senting the angular position of the craft longitudinal relative to the horizon. Then the` summing circuit- 202 output signal could be used to control the lateral position ing ofthis typeVIOL craft. k'Ihe throttle-pitch control intenplay may also be used in landing this type'VTOL craft. `For example, `:the throttle may craft irate of` descent controlled throughpitch commaxi'tlds;`

At that time, the nozzles would be rapidly swungforward f to stop the crafts forward movement. Then, therate of descent would be commanded loop.

embodiments, it is .to be 'understood that the words which have been used are words off description Yrather thanofy limitation and that changes withinthe purview of the 'Yap-vg pendedclaims may he made .without departing from the true scopeand spirit of the invention in itsv broaderY s ver, said maneuver being one which is initiated when the` l craft is flying substantially horizontal to 'the egartlnsaidcraft being ofthe type that lands with its longitudinal axisV substantially perpendicular to the earth comprising means for varying the pitch of said craft, means for varyingthe magnitude of the craft -thrust,l means operable withsaid thrust and pitch varying means responsive when aklanding is to be effected to reduce saidthrust and, at substantially the same time, to increase gradually the craft pitch, and` means operable with saidthnu'stMaryin-g means responsiye (-in pitch) of the craft-longitudinal axis from'a perpendicular relationship with the earth or a signal representing the craft `ground speed (depending n respectively on whether the switch 204 isin position .1f

speed computer 48. WhenV nothing is connected. to i the summing circuit 202. Hence, with the switch 204:` in, Y

FIG. 5 is essentially the'sanie r land the pilot in changinghis.

his control stick; such control stick manipulation f. causes the craft thrust vector to change direction and .pro duce a craft ground speed signal which, when algebraically added tothe pick-olf signal, cancels that signal.k With craft velocity in bringing the craftV be retarded andthe i throughthe throttle'control While the invention has beenl described in its preferred the pitch attitude of verti-y y said craft, means for commanding a rate of descent for said craft, means responsive Whena landing is to be effected to retard said throttle means to ia predetermined value, and, `at substantially the same time, command said craft descent rate, 'and means responsive ata predetermined pitch attitude to command said pitch rate and advance said throttle means to a value approximately equal to the craft Weight;

3. Apparatus rfor controlling during la landing maneuver l the pitch `attitude of a vertical take-off |and landing aircraft `of the type that lands with its longitudinal axis perpendicular to the earth, said landing maneuver being one which is initiated when the craft is flying substantially horizontal to the earth, comprising thrust controlling means, pitch controlling lmeans, means operable with said thrust and pitch controlling means responsive when a landing is to be effected to decrease the craft thrust and increase the craft pitch lso as to maintain fa predetermined craft descent rate, means responsive yat Iapproximately the craft stall angle of attack to increase the craft thrust, and means responsive when the craft pitch is substantially ninety degrees to cease increasing the craft pitch.

4. Apparatus for controlling during a landing maneuver the pitch attitude of a vertical take-off and landing aircraft of the type which takes off and lands With its longitudinal axis perpendicular to the earth, said landing maneuver being one which is initiated lwhen .the craft is flying substantially horizontal to the earth, comprising means defining a vertical to the earth, means for commanding la predetermined craft rate of descent, means for varying the attitude of the craft longitudinal exis, means responsive when said landing is to be made V to reduce the thrust of said craft and, 'at substantially the same time, command said predetermined descent rate, and means responsive -at la predetermined pitch attitude to activate said means for Avarying the longitudinal axis :and thereby align the craft longitudinal axis substantially parallel to the defined vertical, and means responsive 'when the craft has a predetermined angleof attack to increase the craft thrust to a value ap proximately equal to the craftaveight.

5. Apparatus for controlling the pitch attitude of a vertical take-off and landing Iaircraft during a landing maneuver,` said maneuver being one yvvhichis initiated when the craft is flying substantially horizontal to the earth,:said craft being of the type which takes off and lands with its` longitudinal taxis perpendicular to the earth comprising meansproviding -a signal representing a constant rate of descent, means providing a signalrepresenting `a craft pitch yattitude of ninety degrees, means for varying the thrust of said craft, means for moving the control surfaces of said craft, means for moving the craft thrust deflector, means responsive when a landing is to be made to reduce theL thrust of said craft to a predetermined value and `at .substantially the same time, apply said rate of descent signal to said means for moving the lcontrol surfaces of said craft to hold the descent rate, and means responsive at approximately the stall. 'angle of attack of said craft to apply the pitch attitude signal to said means for moving the thrust deffector of said craft to ladjust the craft pitch yattitude accordingly, said last mentioned responsive means also applying at substanti-ally the same time the rate of descent signal to said means for varying the craft thrust to hold the descent rate.

attitude of the craft means, and at substantially the same time,

6. Apparatus for `controlling the pitch attitude of a vertical take-off'and `landing aircraft during a landing maneuver, said maneuver being one Which'is initiated when the craft is flying substantially' horizon-tal to the,

earth, said craft lbeing ofthe type that lands with its` elevators with said elevator'moving means to increase the n craft pitch land thereby maintain therdescent rate coni stant, and means responsive at approximately thej--craft stall yangle of attack to increase the `craft thrust with said thrust varying means and move the craft thrust deflector with said deflector moving means to maintain respectively the descent rate `'constant and the pitching up openastantially the same time, move 'to vary the thrust iof said craft,

tion until vsaid craft longitudinal laxis is substantially perpendicular tothe earth.

7. Apparatus for controlling during a landing maneuver the pitch Iattitude of a craft of the type that perpendicular to the earth, said landing maneuver being one which is initiated when the craft is flying substantially horizontal to ythe' earth, comprising lthrust controlling means, pitch controlling means, means operable |with vertical take-off 'and landing airsaid thrust and pitch controlling means responsive when I' a landing is to be effected to decrease the craft thrust and increaseV the craft pitch so as to maintain a predetermined craft descent rate, means responsivein anticipation of the craft angle of attack to increase the craft thrust, and means responsive when the `craft pitch is substantially ninety degrees to cease increasing the 'craft pitch.

8. Apparatus for controlling they pitch :attitude of a vertical take-off and landing aircraft during a landing maneuver,` said maneuver being one which is initiated when the craft is flying lsubstantially horizontal to the earth, said craft being of the type that takes off and lands with its fore-iand-aft axis perpendicular to the earth comprising means producing a signal representing a commanded craft rate of descent, means producing ya signal representing ia craft pitch `attitude of approximately' ninety' degrees, means responsive `when a vlanding isto be effected to retard the throttle of said craft to Iafpredeter-mined value, and at substantially the same time, drive the elevators of said craft with said commanded rate of descent signal to effect the commanded rate of descent, and means responsive lat substantially the stall angle of yattackto drive the throttle of said craft with said rate of descent signal and drive the thrust defies-tor With said craft pitch attitude signal to effect said pitch attitude'.

9. Apparatuspfor controlling the pitch attitude during'a landing maneuver of va vertical take-off and landing 'aircraft of the type that lands with its longitudinal Yaxis perpendicular to the ground, said landing maneuver'being one which is initiated whenthe craft is flying substantially horizontal to the earth, comprising means operable to move the Icontrol surfaces'of said craft,means operable to move the craft thrust deflector, means operable landing fis to be made to decrease the craft thrust 'with said thrust varying means and at substantially the same time graduallyincrease the craft pitch 1With said control surface moving means so as to keep the descent rate constant, means kresponsive prior to reaching the craft stally angle of `attack to increase the craft thrust 'with said thrust varying means so as to keep said descent rate constant 'after the stall angle of Yattack is reached and, at subthe craft thrust deflectors to keep the craft kpitching up until ya pitch attitude of ninety degrees is reached.

l0. Apparatus for controlling the pitch attitude during* `a landing maneuver of ya vertical take-off and landing move the craft lands with its longitudinal' axis.

means responsive when av 11V aircraft ofthe type that lands with its lforeJand-aft axis perpendicular to the ear-th, said landing maneuver being one'vvhich is initiated when the craft is flying substantially horizontal to the earth, comprising means producing Ia signal representing a commanded craft descent rate, means producing a signal representing a pitch attitude of ninety degrees, means for moving the eleva-tors of said craft, means for moving the thrust deiiector of said craft, means for varying the thrust of said craft, means responsive when a landing is to be effected to reduce the craft thrust with said thrust varying means and apply said descent rate signal to said means for moving the craft, elevators to maintain the descent rate constant byv gradually increasing the craft pitch, and means responsive when Asaid stall angle of lattack is anticipated to apply said descent rate signal to sa1d thrust varying means'and therebyfmfaintain said descent rate constant, said last mentioned responsive means `also applying at substantially the same time that said stall angle of attack is anticipated the pitch rate signal to said thrust deflector moving means to move said thrust deliector and diereby sustain the pitching-up of the craft until the craft foreeandlaft axis is substantially perpendicular to the earth.

ll. Apparatus for controlling the pitch attitude during a landing of maneuver of a vertical take-olf and landing *aircraft -of the type that lands ywith its foreeanddaft axis perpendicular to 4the earth, said landing maneuver being one which is initiated when the craft is ying substantially horizontal to the earth, comprising means pro-.-

ducing a signal representing a commanded craft descent rate of zero feet per second, means producing a signal representing a .pitch attitude of ninety degrees, means for moving the elevators of said craft, means for moving the thrust deiiector of said craft, means kfor varying the thrust of said craft, means responsive when a landing is to be effected lto reduce the craft thrust with said thrust varying means and apply said descent rate signalv to said means for moving the `craft elevators to maintain the descent rate constant by gradually increasing the craft pitch, means responsive Awhen said stall angle of attack is anticipated to apply said ldescent rate signal to said thrust varying means and thereby maintain said descent rate constant, said last mentioned responsive means also applying when said stall angle of attackis anticipated the pitch rate signal to said thrust deflector moving means to move said thrust detlector and thereby sustain the pitching-up of the craft until the craft fore-and-aft axis is sub-V stantially perpendicular 4to the earth, and means for controlling the lateral positioning of the craft over the earth after said craft fore-and-aft axis is made substantially perpendicular to the earth comprising pick-off means producing a 'signal representing lthe displacement Aof the craft control stick, means producing a signal representing the angular 'displacement between the craft longitudinal `axis and a vertical to the earth, and normally receiving said last-named signal but receiving said control stick pick-oft signal when said control stick is operated, the output signal from said 4last-named means being applied to said craft thrust deector moving means to move said thrust deflector and thereby tip said craft from `a subninety degrees, means for stantially perpendicular relationship with the earth cause lateral movement of the craft relative to the earth.' l2. Apparatus for controllingthe-pitch attitude during` s a landing maneuver of a vertical take-off and landing aircraft of the type that perpendicular to the earth, said landing maneuver being one Whichis initiated When the craft is flying substantially horizontal to the earth, comprising means producing y a signal representing a Zero commanded craft descent rate,V means producing a signal representing a pitch attitudefof moving the elevators Y of said craft, means forpmoving craft, means for varying responsive When'a landing is to be effected -to reduce the craft thrust with said thrust varying meansand apply said 1 F1., descent rate signal to said means for moving the craft,

elevators -to maintain the descent rate constant by gradually increasing the craft pitch, means responsive when said stall angle of attack is` anticipated to apply said descent rate signal to said thrust varying means and thereby maintain said descent rate constant, saidV last mentionedrespousive means also applying when ,said stall angle of attackk is anticipated the pitch rate signal to said thrust detlector moving means to move said substantially perpendicular totheearth comprising pickotf means producing a signal representing the displace-y ment of the craft control stick, means producing aV signal representing the craft gro-und speed and summing means receiving -beth said signals and Vproducing a signal rep# 13. Apparatus for controlling the lateral positioningV over the earthof a hovering vertical take-olf and landing aircraft having a vertical gyroscope comprising means .for varying the direction of the craft resultant thrust vector, pick-off means operable with the control stick of` said craft to .produce a signal Vrepresentingthe displacel ment of the stick, means independent of said vertical gyroscope producing asignal representing the [ground speed of said craft, and summing means receiving bothr said signals andl producing-a signal representing-their algebraic sum, said sum signal being applied to said thrust. direction varying means to vary the resultant thrust din` rection in proportion Vto said sum signal.

References Cited in the le of this patent i UNITED -STATES lPATENIS- ronEroNi PATENTS lands with its fore-and-aft axisnv the thrust deliector of said*Y Y the thrust of said craft, means'k 'Y thrust deiiector and thereby y sustain the pitching-up of the craf-t until the craft fore-f. and-aft axis is substantially perpendicular to the earth,y and means for controlling'the lateral positioning'of the craft over'the earthaftersaid craft fore-and-aft axis isf Anderson et al. Q '3,` Y Eggers Nov. 8, 1960 

13. APPARATUS FOR CONTROLLING THE LATERAL POSITIONING OVER THE EARTH OF A HOVERING VERTICAL TAKE-OFF AND LANDING AIRCRAFT HAVING A VERTICAL GYROSCOPE COMPRISING MEANS FOR VARYING THE DIRECTION OF THE CRAFT RESULTANT THRUST VECTOR, PICK-OFF MEANS OPERABLE WITH THE CONTROL STICK OF SAID CRAFT TO PRODUCE A SIGNAL REPRESENTING THE DISPLACEMENT OF THE STICK, MEANS INDEPENDENT OF SAID VERTICAL GYROSCOPE PRODUCING A SIGNAL REPRESENTING THE GROUND SPEED OF SAID CRAFT, AND SUMMING MEANS RECEIVING BOTH SAID SIGNALS AND PRODUCING A SIGNAL REPRESENTING THEIR ALGEBRAIC SUM, SAID SUM SIGNAL BEING APPLIED TO SAID THRUST DIRECTION VARYING MEANS TO VARY THE RESULTANT THRUST DIRECTION IN PROPORTION TO SAID SUM SIGNAL. 